Specific force
Specific force is defined as the force per unit mass.
Specific force is measured in meters/second² (m·s-2) which is the units for acceleration. Specific forces are not coordinate-accelerations, but rather proper accelerations, which are accelerations relative to free-fall. Forces, specific forces, and proper accelerations are the same in all reference frames, but coordinate accelerations are frame dependent. For free bodies, the specific force is the cause of a proper acceleration. For bodies constrained from accelerating, the specific force will not equal the acceleration.
g-force acceleration is a specific force. The acceleration of an object free falling towards the earth depends on the reference frame (it disappears in the free-fall or inertial frame), but any g-force "acceleration" is present in all frames.
Accelerometers on the surface of the Earth measure a constant 9.8 m/s^2 even when they are not accelerating (coordinate acceleration). This is because they measure the proper acceleration produced by the g-force exerted by the ground. Accelerometers measure specific force (proper acceleration, which is the acceleration relative to free-fall. [1], not acceleration.
Hydraulics
In open channel hydraulics, specific force (symbol Fs) has a different meaning:
- Fs = y2/2 + (q2)/gy
where q is the discharge per unit width (q = Q/B) and y is the flow depth.
See also
References
- ^ www.strapdownassociates.com/Accels%20Measure.pdf